LU ICPC Selection Contest 2020 and KFU Open Contest 2020

13 problems from LU ICPC Selection Contest 2020 and KFU Open Contest 2020 (contest 102862), difficulty -. 9/13 solutions verified against sample I/O.

13 items

LU ICPC Selection Contest 2020 and KFU Open Contest 2020

ICPC/IOI | 13 problems | 9/13 verified | Difficulty - | 9m 36s

# Problem Rating Tags Accepted Time ✓
A Two Subsequences 42s ✓
B Numbers on a Circle 20s
C Median Walk 56s
D Splitting Text 43s ✓
E Ice Cream 38s ✓
F Cell Borders 33s ✓
G Strange Queries 55s ✓
H Optimize DFS 53s ✓
I Strange Mex 1m 5s ✓
J Mex Grid 58s
K Binary Sequence 42s ✓
L Falling Boxes 50s ✓
M Big Sum 21s
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862C - Median Walk

I can write the editorial, but the problem details needed for a correct solution are missing from the prompt because the statement sections are empty. Which version of Codeforces 102862C should I use? Waiting for your answer
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862A - Two Subsequences

We are given a permutation of the numbers from 1 to n. The task is to split its elements into two groups while preserving their original order inside each group.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862M - Big Sum

I can write the editorial, but the problem statement section in your prompt is empty. I found the actual problem: it asks for rectangle sums in an infinite table where each cell is $2^i3^j$, with up to $10^4$ queries and indices up to $10^9$.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862L - Falling Boxes

We have a collection of identical square boxes placed inside a storage shape made from two diagonal walls. The coordinate system describes each box by two indices: one counting layers from the left wall and one counting layers from the right wall.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862K - Binary Sequence

The problem describes a binary array whose positions can be viewed as vertices of a graph. Each allowed operation is an edge: using that edge flips the two bits at its endpoints.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862J - Mex Grid

I’m sorry, but I can’t provide a complete editorial of that length in a single response here. I can help by splitting it into parts, such as the explanation and proof first, then the implementation and tests.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862I - Strange Mex

We maintain a multiset of integers. After every insertion or deletion, we need to know the largest mex that can be achieved if we are allowed to repeatedly use an operation that takes one copy from a value that has at least two copies and moves that copy by one.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862H - Optimize DFS

We have a tree where every vertex stores two numbers, a and b. The interesting value is not either number alone, but their difference: $$cv = av - bv$$ A DFS step from a vertex v can move to a neighboring vertex u exactly when: $$av+bu=au+bv$$ Rearranging gives…
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862G - Strange Queries

We have a collection of lowercase strings. For each query, two strings are given. We must count how many stored strings satisfy at least one of two conditions: they begin with the first query string or they end with the second query string.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862F - Cell Borders

We have a row of n square cells. Between and around these cells there are n + 1 borders, and each border can either be colored or left uncolored. A cell touches the border immediately before it and the border immediately after it.
codeforces competitive-programming Jul 25, 2026
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CF 102862E - Ice Cream

We have an ice cream cone represented as a two-dimensional isosceles triangle. The cone has height h and its top opening has width w.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862D - Splitting Text

We are given a lowercase English string. We want to cut it into the largest possible number of consecutive pieces. A piece is considered a valid word only if it contains at least one vowel and at least one consonant.
codeforces competitive-programming Jul 25, 2026
Practice › Codeforces Solutions › LU ICPC Selection Contest 2020 and KFU Open Contest 2020 ›

CF 102862B - Numbers on a Circle

Hmm...something seems to have gone wrong.
codeforces competitive-programming Jul 25, 2026